Single-shot imaging device and method based on structured light coding and transient grating shutter

Abstract

The invention provides a single-shot imaging device and method based on structured light coding and a transient grating shutter. The device comprises an ultrashort pulse laser, a transient event device to be measured, an optical beam splitter, an optical path adjusting unit, a structured light coding unit, an optical beam combiner, a transient grating shutter unit, an imaging unit and a data processing unit which are sequentially arranged in the laser transmission direction, wherein the data processing unit is in communication connection with the imaging unit; an ultrashort pulse laser irradiates a transient event device to be measured to generate signal light to be measured, and the signal light to be measured is split into a plurality of sub-beams by an optical beam splitter; the optical path adjusting unit is used for setting time delay for each sub-beam, modulation coding is carried out through the structured light coding unit, gating of different time slices is carried out through the transient grating shutter unit, and a composite light field image is formed in the imaging unit; and the light field information of each sub-beam at different time is recovered by using the data processing unit, so that femtosecond-magnitude time resolution and high-precision measurement of transient events are realized.

Description

Technical Field

[0001] The present invention relates to the field of laser technology and devices, and in particular to a single-shot imaging device and method based on structured light coding and transient grating shutter. Background Art

[0002] Ultrafast phenomena are widely present in the natural world and scientific and technological research, reflecting many important basic mechanisms in physics, chemistry and biology. Ultrafast phenomena generally occur in two-dimensional space on a time scale from nanoseconds to femtoseconds. Ultrafast optical imaging technology can realize two-dimensional visualization observation of transient evolution processes. It is an important tool for studying ultrafast dynamics and has always attracted extensive attention from researchers in the field of science and technology. For highly repeatable ultrafast phenomena, the classical pump-probe method is usually used to capture the dynamic evolution process of transient events and explore potential influencing mechanisms. However, many ultrafast phenomena are either non-repeatable or difficult to reproduce, such as ultra-intense laser filamentation, component damage, irreversible chemical reactions, etc. In these cases, the pump-probe method is difficult to play a role. In addition, for transient events with low repetition frequency or significant changes between bursts, such as plasma evolution, pump-probe methods not only have low measurement efficiency, but also cannot obtain accurate dynamic evolution information. The pump-probe method is limited to statistical studies under repeatable conditions.

[0003] In order to overcome the limitations of the pump-probe method, researchers have proposed a series of single-shot ultrafast light field imaging techniques in recent years. Single-shot ultrafast light field imaging technology refers to the ability to obtain multiple spatiotemporal resolution information of the entire transient event through only a single exposure. Among them, "single-shot" means that the entire transient event can be captured with a single exposure, "ultrafast" means that time resolution from femtoseconds to nanoseconds can be achieved, "light field" means that spectral information from extreme ultraviolet to far infrared can be detected, and "imaging" means that spatial (x, y) dimension information can be obtained. Single-shot ultrafast light field imaging technology can characterize transient events under a wider range of and more arbitrary conditions, opening the door to the study of non-repeatable and difficult to reproduce ultrafast phenomena, and has become an indispensable tool for understanding basic scientific and technological issues and achieving high-precision and high-efficiency measurements.

[0004] The existing single-shot ultrafast light field imaging measurement technology usually uses ultrashort pulse trains as probe primitives, actively encodes in dimensions such as space, angle, wavelength, polarization or spatial frequency, and then completes the measurement of transient events. This type of measurement method that uses ultrashort pulse trains as illumination probes detects transient events (such as laser-induced plasma), and it is difficult to measure the light field itself. Another type of single-shot ultrafast light field imaging measurement technology does not require active illumination, and ultrafast time resolution is achieved by ultrafast photodetectors. Although it can measure the light field, it is difficult to take into account the measurement requirements of wide spectral range and high temporal and spatial resolution. Ultrafast light field detectors mainly include framing cameras based on fast electronics principles, in-situ storage electronic shutter cameras, and high-speed sampling cameras. Among them, the microchannel plate traveling wave gating framing camera is relatively mature. Its basic principle is to control the gating of extremely narrow pulse width electrical pulses and amplify images at different times. The currently developed ultra-high-speed MCP framing camera can achieve a minimum gate width of 200ps. However, due to the difficulty of the spectral response of the photocathode in the infrared band, the MCP framing camera is difficult to cover the wide spectrum measurement requirements from ultraviolet to infrared.

[0005] Therefore, the prior art needs to be further developed. Summary of the invention

[0006] The purpose of the present invention is to overcome the above-mentioned technical deficiencies and provide a single-shot imaging device and method based on structured light coding and transient grating shutter to solve the problems existing in the prior art, aiming to achieve single-shot sub-high spatiotemporal resolution imaging of transient events while having a wide spectral response range and a simplified system structure.

[0007] To achieve the above technical objectives, according to a first aspect of the present invention, the present invention provides a single-shot imaging device based on structured light coding and a transient grating shutter, comprising:

[0008] An ultrashort pulse laser, a transient event device to be measured, an optical beam splitter, an optical path adjustment unit, a structured light encoding unit, an optical beam combiner, a transient grating shutter unit, an imaging unit, and a data processing unit in communication with the imaging unit are sequentially arranged along the laser transmission direction.

[0009] Specifically, the ultrashort pulse laser is used to illuminate the transient event device to be measured, and generate a signal light to be measured that carries the information to be measured.

[0010] Specifically, the optical beam splitter is used to split the signal light to be measured into multiple sub-beams.

[0011] Specifically, the optical path adjustment unit is arranged in the optical path where each sub-beam is located, and the optical path adjustment unit is used to set a different time delay for each sub-beam.

[0012] Specifically, the optical path adjustment unit includes at least any one of the following:

[0013] A combination of an adjustable optical delay line, a reflector set and an electric translation stage.

[0014] Specifically, the structured light encoding unit includes a plurality of gratings located at different spatial orientations, and the gratings are used to perform spatial frequency domain modulation encoding on each sub-beam.

[0015] Specifically, the optical beam combiner is used to combine the modulated and coded sub-beams;

[0016] The transient grating shutter unit includes a Kerr medium and a pump light source;

[0017] The pump light source is used to generate two beams of pump light, which interfere in the Kerr medium to form a transient grating, and then the encoded sub-beams are directed to the transient grating for gating at different time slices.

[0018] Specifically, the imaging unit is used to receive each sub-beam after being gated by the transient grating shutter, and form a composite light field image;

[0019] The data processing unit is used to perform frequency domain analysis on the composite light field image, separate and restore the light field information of each sub-beam at different time slices.

[0020] According to a second aspect of the present invention, a single-shot imaging method based on structured light coding and transient grating shutter is provided, comprising:

[0021] S100, using an ultrashort pulse laser to illuminate a transient event device to be measured, generating a signal light to be measured that carries information to be measured, and using an optical beam splitter to split the signal light to be measured into a plurality of sub-beams;

[0022] S200, using an optical path adjustment unit to set different time delays for each sub-beam;

[0023] S300, performing spatial frequency domain modulation encoding on each sub-beam using gratings at different spatial orientations in a structured light encoding unit to form an encoded sub-beam;

[0024] S400, combining the encoded sub-beams through an optical beam combiner to form a first combined beam;

[0025] S500, passing the first combined beam through a transient grating shutter unit, and using the transient grating shutter unit to perform gating on different time slices of each encoded sub-beam;

[0026] S600, directing each selected sub-beam to an imaging unit to form a composite light field image;

[0027] S700 , using a data processing unit to perform frequency domain analysis on the composite light field image, and to separate and restore the light field information of each sub-beam at different time slices.

[0028] Specifically, the data processing unit is used to perform frequency domain analysis on the composite light field image, and separate and restore the light field information of each sub-beam at different time slices, including:

[0029] The data processing unit is used to perform Fourier transform, spatial frequency shift, low-pass filtering, and inverse Fourier transform on the composite light field image, thereby separating and restoring the light field information of each sub-beam.

[0030] Beneficial effects:

[0031] 1. The present invention realizes single-shot ultrafast optical imaging based on structured light coding and transient grating shutter gating. It can capture multiple spatiotemporally resolved images of ultrafast phenomena in a single exposure through frequency domain recognition and analysis. The number of image frames is further increased by structured light coding multiplexing. The transient grating shutter gating can realize femtosecond time resolution. Combined with a high spatial resolution optical system, high-precision measurement of transient events is realized. The transient grating shutter uses two beams of pump light to interfere in a Kerr medium to generate a transient grating to diffract the signal light to achieve gating. The diffraction signal appears in the direction of wave vector matching, which has the advantages of background-free detection and high extinction ratio.

[0032] 2. The present invention is based on the principle of image transfer, realizes multi-framing imaging in spatial frequency domain coding, does not rely on dispersion coding, retains all spectral information of transient events to be measured, has full spectrum compatibility, and the spectral range depends on the spectral transmittance of the optical element, so it can cover a wide spectral range from infrared to ultraviolet, is suitable for a variety of spectral measurement needs, and provides a powerful tool for ultrafast phenomenon research. In addition, the single-shot imaging device in the present invention is simple in composition, greatly reduces the cost, and greatly improves the availability and reliability of the present invention.

[0033] 3. Based on the single-shot ultrafast imaging device provided by the present invention, the placement of the transient event to be measured can be eliminated, thereby realizing ultrafast time-resolved imaging of the spatiotemporal structure of the laser pulse itself, which can be widely used in the study of non-repetitive and difficult-to-reproduce ultrafast phenomena, and is not limited to transient events or the laser itself, greatly expanding the application scenarios of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the overall structure of a single-shot imaging device based on structured light coding and transient grating shutter provided in a specific embodiment of the present invention;

[0035] Figure 2 is a schematic diagram of a transient grating shutter provided in a specific embodiment of the present invention;

[0036] Figure 3 It is a schematic diagram of the optical path structure of single-shot imaging based on structured light coding and transient grating shutter provided in a specific embodiment of the present invention;

[0037] Figure 4 is a schematic diagram of the time resolution of the system when H-ZF73 is used as the optical Kerr medium provided in a specific embodiment of the present invention;

[0038] Figure 5 It is a simulation diagram of the influence of the thickness of the Kerr medium and the light intensity on the diffraction efficiency of the transient grating shutter provided in a specific embodiment of the present invention;

[0039] Figure 6 It is a composite overlapping image carrying information to be measured at different times provided in a specific embodiment of the present invention;

[0040] Figure 7 It is a spatial spectrum distribution diagram corresponding to a composite overlapping image carrying information to be measured at different times provided in a specific embodiment of the present invention;

[0041] Figure 8 It is a spatial frequency domain frequency shift diagram of the composite overlapping light field spectrum provided in a specific embodiment of the present invention;

[0042] Fig. 9 It is a spectrum diagram of low-pass filtering of the composite overlapping light field spectrum provided in a specific embodiment of the present invention;

[0043] Fig.10 is a spatial spectrum diagram of the first moment separated and provided in a specific embodiment of the present invention;

[0044] Fig.11 is a transient image corresponding to the separated spatial spectrum diagram at the first moment provided in a specific embodiment of the present invention;

[0045] Fig.12 is a spatial spectrum diagram of the second moment separated and provided in a specific embodiment of the present invention;

[0046] Fig.13 is a transient image corresponding to the separated spatial spectrum diagram at the second moment provided in a specific embodiment of the present invention;

[0047] Fig.14 is a flow chart of a single-shot imaging method based on structured light coding and transient grating shutter provided in a specific embodiment of the present invention;

[0048] Wherein, the reference numerals of the above-mentioned drawings are as follows:

[0049] 1. Ultrashort pulse laser; 2. Transient event device to be measured; 3. Optical beam splitter; 4. Optical path adjustment unit; 5. Structured light encoding unit; 6. Optical beam combiner; 7. Transient grating shutter unit; 8. Imaging unit; 9. Pump beam splitter; 10. Signal light path adjustment unit; 11. First pump light path adjustment unit; 12. Second pump light path adjustment unit; 13. First beam splitter; 14. Second beam splitter; 15. Third beam splitter; 16. Fourth Beam splitter; 17, focusing lens; 18, first reflector; 19, second reflector; 20, height-tunable climbing mirror assembly; 21, fifth beam splitter; 25, sixth reflector; 26, Kerr medium; 27, pinhole aperture; 401, first optical path adjustment unit; 402, second optical path adjustment unit; 403, third optical path adjustment unit; 501, first structured light coding unit; 502, second structured light coding unit; 503, third structured light coding unit. DETAILED DESCRIPTION

[0050] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is clearly and completely described below in conjunction with the accompanying drawings of the present invention. Based on the embodiments in this application, other similar embodiments obtained by ordinary technicians in this field without making creative work should all fall within the scope of protection of this application. In addition, the directional words mentioned in the following embodiments, such as "up", "down", "left", "right", etc., are only reference to the directions of the accompanying drawings. Therefore, the directional words used are used to illustrate rather than limit the invention.

[0051] The present invention will be further described below in conjunction with the accompanying drawings and preferred embodiments.

[0052] See also Figure 1 This embodiment provides a single-shot imaging device based on structured light coding and transient grating shutter, including:

[0053] An ultrashort pulse laser 1, a transient event device to be measured 2, an optical beam splitter 3, an optical path adjustment unit 4, a structured light encoding unit 5, an optical beam combiner 6, a transient grating shutter unit 7, an imaging unit 8, and a data processing unit connected to the imaging unit 8 are sequentially arranged along the laser transmission direction.

[0054] It can be understood that the working process of the single-shot imaging device in this embodiment includes: irradiating the transient event device 2 to be measured by an ultrashort pulse laser 1, dividing the signal light carrying the information to be measured into multiple sub-beams by using the optical beam splitter 3, and setting different time delays for each sub-beam by the optical path adjustment unit 4, and then each sub-beam is modulated and encoded by the grating in different spatial orientations in the structured light encoding unit 5. The encoded structured light sub-beams are combined by the optical beam combiner 6 and incident on the transient grating shutter of the transient grating shutter unit 7. Under the control of the pump light, the transient grating shutter realizes the gating of different time slices of each sub-beam, and finally images are formed on the imaging unit 8. The light field information at different times is restored through the frequency domain recognition and analysis technology of the data processing unit.

[0055] See also Figure 1 The optical beam splitter 3 may include beam splitters arranged on a plurality of different signal light branches, such as Figure 1 301, 302, ... 30n (n is a natural number), the optical path adjustment unit 4 may include an optical path adjustment unit arranged in a plurality of signal light branches, such as Figure 1 401, 402, 40n, the structured light encoding unit 5 may include structured light encoding units arranged in a plurality of signal light branches, such as Figure 1 501, 502, …50n.

[0056] Specifically, the ultrashort pulse laser 1 is used to illuminate the transient event device 2 to be measured, and generate a signal light to be measured that carries the information to be measured.

[0057] Furthermore, the transient events to be measured include ultrafast phenomena in the fields of physics and chemistry, such as plasma evolution, crystal phase transition, irreversible chemical reactions and other transient evolution processes. The single-shot imaging device in this embodiment can observe the details of these transient events, understand their occurrence mechanism, intermediate state and other information, and thus conduct in-depth research on the transient evolution process of related transient events.

[0058] Specifically, the optical beam splitter 3 is used to split the signal light to be measured into multiple sub-beams.

[0059] In a specific embodiment, the optical beam splitter 3 is composed of a series of beam splitters with different splitting ratios, which are used to split the signal light carrying the information to be measured into multiple sub-beams. Preferably, the splitting ratio of the beam splitter is adjusted to make the energy of each sub-beam as equal as possible, so as to ensure the accuracy and consistency of subsequent operations. For the structured light coding unit 5, if the energy difference of the sub-beams is too large, it may cause inaccurate coding information during the coding process, affecting the coding effect. Making the energy of each sub-beam as equal as possible helps to ensure the stability of the operation of the entire single-shot ultrafast imaging device.

[0060] See also Figure 3The optical beam splitter 3 includes a first beam splitter 13 , a second beam splitter 14 , a third beam splitter 15 and a fourth beam splitter 16 .

[0061] Specifically, the optical path adjustment unit 4 is disposed in the optical path where each sub-beam is located, and the optical path adjustment unit 4 is used to set a different time delay for each sub-beam.

[0062] Specifically, the optical path adjustment unit 4 includes at least any one of the following:

[0063] A combination of an adjustable optical delay line, a reflector set and an electric translation stage.

[0064] In a specific implementation, the optical path adjustment unit 4 is arranged in the optical path of each sub-beam, and is generally composed of a reflector group and an electric displacement platform, and can also be composed of an adjustable optical path delay line, for setting different time delays for each sub-beam.

[0065] See also Figure 3 , the optical path adjustment unit 4 includes a first optical path adjustment unit 401, a second optical path adjustment unit 402, and a third optical path adjustment unit 403;

[0066] Specifically, the structured light encoding unit 5 includes a plurality of gratings located at different spatial orientations, and the gratings are used to perform spatial frequency domain modulation encoding on each sub-beam.

[0067] In a specific implementation scheme, the structured light coding unit 5 can select a Ronchi grating or a sinusoidal amplitude grating, and each sub-beam has a different spatial orientation. The different spatial orientation coding is to avoid the far-field of the encoded sub-beams from overlapping in the spatial frequency domain and affecting the spatial frequency domain resolution. This different spatial orientation coding is of great significance, because during the imaging process, if the far-field of the encoded sub-beams overlaps in the spatial frequency domain, it will have an adverse effect on the resolution of the spatial frequency domain, and thus interfere with the entire imaging effect. Therefore, by assigning different spatial orientation codes to each sub-beam, this situation can be effectively avoided, thereby ensuring that the information of each sub-beam in the spatial frequency domain can be accurately distinguished, providing a clear and accurate coding information basis for subsequent imaging measurements.

[0068] Specifically, the optical beam combiner 6 is used to combine the modulated and coded sub-beams;

[0069] Furthermore, the optical beam combiner 6 is generally composed of a multi-stage beam combiner.

[0070] The transient grating shutter unit 7 includes a Kerr medium 26 and a pump light source;

[0071] The pump light source is used to generate two beams of pump light, which interfere in the Kerr medium 26 to form a transient grating, and then the encoded sub-beams are directed to the transient grating for gating at different time slices.

[0072] In a specific implementation scheme, the Kerr medium 26 can select H-ZF73, which has many excellent properties. For example, it has a high nonlinear refractive index, which enables it to produce obvious optical nonlinear effects when interacting with pump light, which plays a key role in the formation of transient gratings. The medium has a fast polarization response speed and can quickly respond to the electric field changes caused by the pump light, thereby ensuring that the transient grating can be formed in a very short time, which is very important for realizing the function of ultrafast time resolution. H-ZF73 also has the advantage of a good transmission surface, which means that light can maintain good propagation characteristics when passing through the medium, reducing adverse effects such as light scattering and deformation, which is beneficial to improving the imaging quality and measurement accuracy of the entire system and can achieve ultrafast time resolution.

[0073] See also Figure 2 , inside the Kerr medium 26, the wave vectors of the two pump lights (k1 and k2) and the probe signal light (k3) are arranged at the three vertices of the square, and the fourth diffracted light signal light will appear at the remaining vertices of the square. The four wave vectors automatically meet the phase matching conditions of four-wave mixing. The transient grating shutter utilizes two high-power pump lights to interfere and induce a transient refractive index structure in the Kerr medium 26. The third signal light is incident on the transient refractive index structure in the Kerr medium 26 to modulate and generate the fourth diffracted light. The fourth diffracted light corresponds to the third signal light and carries the same modulation information of the transient event to be measured as the third light. The direction of the fourth diffracted light is different from that of the first three lights. The transient grating time shutter can achieve local-free detection and has a high extinction ratio. Compared with the Kerr gate, the diffraction switch is more efficient and does not require a high polarization extinction ratio device, which further simplifies the structure of the entire optical system, reduces the construction cost, and greatly improves the stability and adaptability of the optical system in different environments.

[0074] Specifically, the imaging unit 8 is used to receive each sub-beam after being gated by the transient grating shutter, and form a composite light field image;

[0075] The data processing unit is used to perform frequency domain analysis on the composite light field image, separate and restore the light field information of each sub-beam at different time slices.

[0076] See also Figure 6-Figure 13 The working principle of the present invention is explained below by using theoretical analysis and simulation to verify the physical feasibility of the single-shot ultrafast imaging technology solution based on structured light encoding and transient grating shutter gating:

[0077] Assume that the signal light I(x, y, t) to be measured carrying the transient event information is split into two beams by the optical beam splitter 3, which are represented as I 10 (x,y,t) and I 20 (x, y, t), a thin sinusoidal amplitude grating is used to encode the beamlet. The first grating and the second grating can be described as:

[0078]

[0079]

[0080] Among them, G1(x,y) represents the first grating, G2(x,y) represents the second grating, x, y represent the two-dimensional space coordinates, corresponding to the horizontal and vertical directions respectively, t represents the time coordinate, I 10 (x, y, t) represents the first signal light to be measured, I 20 (x, y, t) represents the second signal light to be measured, m represents the amplitude, Represents phase;

[0081] The grating-encoded light field can be described as:

[0082] I1(x,y,t)=I 10 (x,y,t)G1(x,y)

[0083] I2(x,y,t)=I 20 (x,y,t)G2(x,y), (2)

[0084] Where, I1(x, y, t) represents the first light field, and I2(x, y, t) represents the second light field;

[0085] After being selected by the transient grating shutter unit 7, the light fields at two different moments are:

[0086] ΔI1(x,y,t)=I 10 (x,y,Δt1)G1(x,y)

[0087] ΔI2(x,y,t)=I 20 (x,y,Δt2)G2(x,y), (3)

[0088] Wherein, ΔI1(x, y, t) represents the light field at the first moment, ΔI2(x, y, t) represents the light field at the second moment, Δt1 and Δt2 represent the first moment and the second moment respectively;

[0089] The two beams are combined and received by the same camera. The light field received by the camera is expressed as:

[0090] ΣI(x,y,t)=ΔI1(x,y,t)+ΔI2(x,y,t), (4)

[0091] Perform Fourier transform on the signal received by the camera, and the light field frequency domain is represented as:

[0092]

[0093] Among them, AF(ξ,η) represents the light field frequency domain, ξ and η represent discrete variables in the spatial frequency domain, Respectively represent the Fourier transform of the light field at the first moment and the second moment;

[0094] It can be seen from formula (5) that after the sinusoidal grating modulation encoding, there are 0-level and ±1-level light fields at different times on the spectrum plane. By using sinusoidal gratings of different frequencies and orientations, the ±1-level of the first light field and the second light field are separated in the spectrum space. After bandpass filtering, the separated light field is obtained by inverse Fourier transform, that is, the time-resolved light field.

[0095] like Figure 6-Figure 13 As shown in Figure 1, the simulation of the encoding and parsing process of transient events further simulates the entire process of encoding, acquiring, frequency shifting, low-pass filtering and restoration of light field images: First, scenes of transient events with large feature differences at different times (the first time and the second time) are selected, which are also used as two light fields at different times after beam splitting. The original frequency distributions of the two images are both located near the zero frequency. The light field images at two different times are modulated and encoded by gratings in different orientations and then overlapped. The composite overlapping light field and its spectrum are shown in Figure 1. Figure 6 and Figure 7 As shown in the figure, the center of the spatial frequency domain is the spectrum of the first moment and the second moment mixed together, which is difficult to distinguish; the four peripheral spectrum areas are the ±1-level spectrum of the separated first moment and the second moment, respectively. By frequency shifting and low-pass filtering the composite overlapping light field spectrum, the separated spectrum of the first moment and the second moment can be obtained. Figure 8 is the spatial frequency domain frequency shift diagram of the composite overlapping light field spectrum. Fig. 9 The spectrum of the composite overlapping light field spectrum is low-pass filtered, and then the inverse Fourier transform is used to restore the separated transient events at different times. Fig.10 is the spatial spectrum diagram of the first moment separated, Fig.11 is the transient image corresponding to the separated spatial spectrum at the first moment, Fig.12 is the separated spatial spectrum diagram of the second moment, Fig.13 It is the transient image corresponding to the separated spatial spectrum diagram at the second moment.

[0096] In summary, theoretical analysis and simulations show that the single-shot ultrafast imaging technology solution based on structured light coding and transient grating shutter gating is physically feasible. It can not only image and measure typical transient events such as laser-induced plasma evolution, but also work together in this process. The structured light coding unit can accurately encode the signal light related to the transient event, and the transient grating shutter unit can accurately select the appropriate time slice, so as to clearly capture the evolution of plasma in a very short time, providing a powerful imaging method for studying the physical properties of plasma. This technical solution also has the ability to image the light field itself. By imaging the light field itself, it is possible to deeply explore important characteristics such as the distribution and intensity change of the light field, providing a new perspective and tool for the study of the light field, breaking through the limitations of existing technologies, with strong scalability and a high upper limit of measurement.

[0097] See also Figure 3-Figure 5 , the specific parameter design and selection scheme of the single-shot imaging device based on structured light coding and transient grating shutter proposed in this embodiment, as well as the working mechanism of the device are described in detail below through a specific example:

[0098] The overall design of the device is as follows:

[0099] The ultrashort pulse laser 1 is divided into signal light and pump light by a pump beam splitter 9. The signal light irradiates the transient event device 2 to be measured. The signal light to be measured carrying the transient event is divided into three sub-beams by a series of optical beam splitters 3. Subsequently, an electric displacement platform and two reflectors are used as an optical path adjustment unit 4 to set three different time delays for the three sub-beams, respectively selecting 0ps / 0.3ps / 0.6ps; then, the three sub-beams are modulated and encoded in the spatial frequency domain by gratings with spatial orientations of 0° and ±8.3°, forming encoded structured photons. The coded sub-beams are combined by the beam combiner and then incident on the H-ZF73 optical Kerr medium 26. In addition, the pump light is divided into two beams by the series optical beam splitter 3. The optical path length adjustment unit of the pump light adjusts the optical path length of the first pump light and the second pump light to be equal, and the laser energy is as consistent as possible. The optical path length adjustment unit of the signal light 10 is used to adjust the optical path length delay of the three structured photon beams as a whole to achieve strict synchronization with the pump light, that is, the 0 time of the pump light coincides with the 0 time of the signal light; then, the two pump lights are controlled to interfere in the Kerr medium 26 to generate a transient grating. The diffraction of the three structured photon beams to be measured by the transient grating is used to achieve time gating, and the transient events at different times are intercepted; finally, the light field information after gating is imaged on the camera, and the light field images at three different times are restored by the frequency domain recognition and analysis unit.

[0100] The following is a detailed explanation:

[0101] like Figure 3As shown, an ultrashort pulse laser with a central wavelength of 1030nm, a pulse width of 1ps, and a diameter of 3mm is used as the ultrashort pulse laser 1. The ultrashort pulse laser is divided into signal light and pump light by a pump beam splitter 9. The splitting ratio of the pump beam splitter 9 is 30:70, 70% of the laser energy is used as pump light, and 30% of the laser energy is used as signal light.

[0102] After the signal light irradiates the transient event device 2 to be measured, it is divided into three sub-beams by the optical beam splitter 3. The timing of each sub-beam is precisely adjusted by the optical path adjustment unit 4, and the optical path adjustment unit 4 includes a first optical path adjustment unit 401, a second optical path adjustment unit 402, and a third optical path adjustment unit 403, which are respectively arranged on the optical paths where the three sub-beams are located; then, the signal light is respectively adjusted and encoded in the spatial frequency domain by the structured light encoding unit 5, and the optical paths where the three sub-beams are located are respectively provided with a first structured light encoding unit 501, a second structured light encoding unit 502, and a third structured light encoding unit 503, the optical path adjustment unit 4 is composed of an electric translation stage and two 90° reflectors, the structured light encoding unit 5 uses a 10lp / mm Ronchi grating encoding, the focal length of the focusing lens 17 is 150mm, and the separation distance of the 0th order diffraction and the 1st order diffraction in the far-field spectrum space is 1.55mm. In order to achieve three-part division, the focal spots of different sub-beams do not overlap, the offset angle of the grating in the direction of the beam cross section (vertical incident direction of light) is 8.3°, and the spatial orientations of the three gratings are 0 and ±8.3° respectively. Since the commercial grating specifications are square (1 inch * 1 inch), in order to achieve precise adjustment of the spatial orientation of the grating, a custom square-circular adapter fixture is used. Here, a 2-inch circular wave plate frame is embedded with a 1-inch square grating, which is fixed in the middle by a fixture adapter. There is a difference in time delay between each sub-beam of the signal light. By adjusting the electric translation stage, the time delay relative to the pump light is set to 0ps, 0.3ps and 0.6ps. Finally, the three sub-beams after delay encoding by the optical combiner 6 are coaxially combined, and the spatial incident angle is adjusted by the first reflector 18 and the second reflector 19, and the incident on the Kerr medium 26.

[0103] The pump light is divided into the first pump light and the second pump light by the fifth beam splitter 21, and the first pump light optical path adjustment unit 11 and the second pump light optical path adjustment unit 12 are respectively subjected to precise delay synchronization adjustment. Subsequently, the first pump light and the second pump light are respectively adjusted in spatial incident angle by the highly tunable climbing mirror group 20 and the sixth reflector 25, and are incident on the Kerr medium 26. It should be noted that the first pump light, the second pump light and the signal photon beam need to meet the four-wave mixing phase matching condition. In the design of this scheme, the spatial angle is cleverly designed, and the diamond spatial orientation is adopted. The first pump light and the signal photon beam only need to adjust the angle in the horizontal direction, and the second pump light only needs to adjust the angle in the vertical direction, which reduces the complexity of angle adjustment and is more conducive to meeting the phase matching condition.

[0104] Kerr medium 26 is H-ZF73 with a high nonlinear refractive index coefficient of 87e-7cm 2 / GW. like Figure 5 As shown in the figure, based on the Kogelnik theory, the diffraction efficiency variation of H-ZF73 medium is simulated under the coordinated change of medium thickness and power density. 2 Under pump light excitation, the switching efficiency of 10mm, 20mm and 30mm thick H-ZF73 is 0.26, 0.76 and 1 respectively. With the increase of dielectric thickness and pump light power density, the switching efficiency increases. When the pump light is expanded, the power density of the pump light decreases. The decrease in switching efficiency can be compensated by increasing the dielectric thickness. When the dielectric thickness is 0-40mm and the power density is 0-3GW / cm 2 Within the parameter range, the diffraction efficiency of H-ZF73 changes by 1 cycle, the processing technology of H-ZF73 is relatively mature, and the surface shape is good. Considering the defects of CS2 such as micro-toxicity and volatility, and the surface shape of liquid transmission is not as good as that of solid, the present invention adopts H-ZF73 medium. In order to construct the transient grating shutter unit 7, the H-ZF73 glass is placed on a precision optical platform, and its position is adjusted to ensure that the pump light and the signal light can be accurately focused inside the glass.

[0105] The time response characteristics of H-ZF73 were tested by step scanning method. The test equipment includes electric displacement platform, energy calorimeter, camera and oscilloscope. First, adjust the signal light and pump light time to coincide, observe the time gating signal on the energy calorimeter (camera or oscilloscope), change the pump light excitation time through the electric displacement platform, synchronously test the response amplitude of the signal light, and measure the time response curve of H-ZF73 by scanning point by point. Figure 4 When H-ZF73 is used as the optical Kerr medium 26, the time resolution of the system is 1.57 ps (half-maximum width) and 5.77 ps (10% bottom width).

[0106] The encoding imaging optical path is designed based on the single-lens 2f imaging principle. The object plane is located at the grating. The distance between the structured light encoding unit 5 of each sub-beam and the optical Kerr medium 26 is equal, which is 2 times the focal length. Placing a camera at 2 times the focal length behind the optical Kerr medium 26 can realize the imaging of the signal light to be measured in different time segments. Based on the image transfer imaging principle, the adaptation of the wide spectrum light source can be realized, which is not limited to a specific wavelength range and is suitable for a variety of spectral measurement needs. In addition, a small hole diaphragm 27 is placed in front of the imaging measurement center to filter out stray light other than diffracted light, so as to achieve high signal-to-noise ratio and background-free detection.

[0107] It should be noted here that the present invention realizes single-shot ultrafast optical imaging based on structured light coding and transient grating shutter gating. Through frequency domain recognition and analysis, multiple time-space resolution images of the entire light field evolution can be captured in a single exposure. The number of image frames is further increased by structured light coding multiplexing. The transient grating shutter gating can achieve femtosecond time resolution. Combined with a high-spatial-resolution optical system, high-precision measurement of transient events is achieved. The transient grating shutter uses two beams of pump light to interfere in a Kerr medium to generate a transient grating to diffract the signal light to achieve gating. The diffraction signal appears in the direction of wave vector matching, which has the advantages of background-free detection and high extinction ratio. In addition, the single-shot ultrafast imaging system provided by the present invention can be used to detect the light source in a short time. The imaging device can eliminate the need to place a transient event to be measured, and can realize ultrafast time-resolved imaging of the spatiotemporal evolution of the laser pulse itself, greatly expanding the application scope of the present invention. The present invention is based on the image transfer principle, realizes multi-frame imaging in spatial frequency domain coding, does not rely on dispersion coding, retains all spectral information of the transient event to be measured, has full spectrum compatibility, and the spectral range depends on the spectral transmittance of the optical element, so it can cover a wide spectral range from infrared to ultraviolet, is suitable for a variety of spectral measurement needs, and provides a powerful tool for ultrafast phenomenon research. The single-shot imaging device in the present invention is simple in composition, greatly reduces the cost, and greatly improves the availability and reliability of the present invention.

[0108] See also Fig.14 This embodiment provides a single-shot imaging method based on structured light coding and transient grating shutter, the method comprising:

[0109] S100, using an ultrashort pulse laser 1 to illuminate a transient event device 2 to be tested, generating a signal light to be tested that carries information to be tested, and using an optical beam splitter 3 to split the signal light to be tested into a plurality of sub-beams;

[0110] S200, using the optical path adjustment unit 4 to set different time delays for each sub-beam;

[0111] S300, performing spatial frequency domain modulation encoding on each sub-beam using gratings at different spatial orientations in the structured light encoding unit 5 to form an encoded sub-beam;

[0112] S400, combining the encoded sub-beams through an optical beam combiner 6 to form a first combined beam;

[0113] S500, passing the first combined beam through the transient grating shutter unit 7, and using the transient grating shutter unit 7 to perform gating of different time slices on each encoded sub-beam;

[0114] S600, directing each selected sub-beam to the imaging unit 8 to form a composite light field image;

[0115] S700 , using a data processing unit to perform frequency domain analysis on the composite light field image, and to separate and restore the light field information of each sub-beam at different time slices.

[0116] Specifically, the data processing unit is used to perform frequency domain analysis on the composite light field image, and separate and restore the light field information of each sub-beam at different time slices, including:

[0117] The data processing unit is used to perform Fourier transform, spatial frequency shift, low-pass filtering, and inverse Fourier transform on the composite light field image, thereby separating and restoring the light field information of each sub-beam.

[0118] It can be understood that the data processing unit mainly includes frequency domain calculation processes such as Fourier transform, spatial frequency shift, low-pass filtering, and Fourier inverse transform, which are used to perform frequency domain analysis on the composite light field image, separate and restore the light field information of each sub-beam. After each sub-beam is modulated by gratings in different orientations, there are 0-level and ±1-level on the spatial spectrum surface. Due to the different orientations of each sub-beam, the ±1-level of the sub-beam is separated on the spectrum surface. In the frequency domain analysis, after the ±1-level bandpass filtering of each sub-beam, the Fourier inverse transform can obtain the separated sub-beam light field. In addition, by eliminating the placement of the transient event to be measured, ultrafast time-resolved imaging of the spatiotemporal evolution of the laser pulse itself can be achieved, which greatly expands the application scenarios of the present invention.

[0119] It should be noted here that the present invention realizes single-shot ultrafast optical imaging based on structured light coding and transient grating shutter gating. Through frequency domain recognition and analysis, multiple time-space resolved images of the entire light field evolution can be captured in a single exposure. The number of image frames is further increased by structured light coding multiplexing. The transient grating shutter gating can achieve femtosecond time resolution. Combined with a high spatial resolution optical system, high-precision measurement of transient events is achieved. The transient grating shutter uses two beams of pump light to interfere in a Kerr medium to generate a transient grating to diffract the signal light to achieve gating. The diffraction signal appears in the direction of wave vector matching, which has the characteristics of background-free detection. The invention has the advantages of high extinction ratio, and based on the single-shot ultrafast imaging device provided by the invention, it is possible to eliminate the need to place a transient event to be measured, and to achieve ultrafast time-resolved imaging of the spatiotemporal evolution of the laser pulse itself, greatly expanding the application scope of the invention. The invention is based on the image transfer principle, and realizes multi-frame imaging in spatial frequency domain coding, does not rely on dispersion coding, retains all spectral information of the transient event to be measured, has full spectrum compatibility, and the spectral range depends on the spectral transmittance of the optical element, so it can cover a wide spectral range from infrared to ultraviolet, is suitable for a variety of spectral measurement needs, and provides a powerful tool for ultrafast phenomenon research.

[0120] The present invention is not limited to the aforementioned specific implementations, nor is it limited to the aforementioned application scenarios, and can be applied to any filtering scenario, and the present invention is not limited to this. In addition, the present invention extends to any new features or any new combination disclosed in this specification, and any new method or process steps or any new combination disclosed.

[0121] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0122] Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0123] The various technical features described above can be combined arbitrarily. Although all possible combinations of these technical features are not described, any combination of these technical features should be considered to be covered by this specification as long as there is no contradiction in such combination.

[0124] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A single-shot imaging device based on structured light coding and transient grating shutter, characterized in that: include: An ultrashort pulse laser (1), a transient event device to be measured (2), an optical beam splitter (3), an optical path adjustment unit (4), a structured light encoding unit (5), an optical beam combiner (6), a transient grating shutter unit (7), an imaging unit (8), and a data processing unit communicatively connected to the imaging unit (8) are sequentially arranged along a laser transmission direction.

2. The single-shot imaging device based on structured light coding and transient grating shutter according to claim 1, characterized in that: The ultrashort pulse laser (1) is used to irradiate the transient event device (2) to be measured, and generate a signal light to be measured that carries information to be measured.

3. The single-shot imaging device based on structured light coding and transient grating shutter according to claim 1, characterized in that: The optical beam splitter (3) is used to split the signal light to be measured into a plurality of sub-beams.

4. The single-shot imaging device based on structured light coding and transient grating shutter according to claim 3, characterized in that: The optical path adjustment unit (4) is arranged in the optical path where each sub-beam is located, and the optical path adjustment unit (4) is used to set a different time delay for each sub-beam.

5. The single-shot imaging device based on structured light coding and transient grating shutter according to claim 4, characterized in that: The optical path adjustment unit (4) comprises at least any one of the following: A combination of an adjustable optical delay line, a reflector set and an electric translation stage.

6. The single-shot imaging device based on structured light coding and transient grating shutter according to claim 5, characterized in that: The structured light encoding unit (5) comprises a plurality of gratings located at different spatial orientations, and the gratings are used to perform spatial frequency domain modulation encoding on each sub-beam.

7. The single-shot imaging device based on structured light coding and transient grating shutter according to claim 6, characterized in that: The optical beam combiner (6) is used to combine the modulated and coded sub-beams; The transient grating shutter unit (7) comprises a Kerr medium (26) and a pump light source; The pump light source is used to generate two beams of pump light, which interfere in the Kerr medium (26) to form a transient grating, and then the encoded sub-beams are directed to the transient grating for gating at different time slices.

8. The single-shot imaging device based on structured light coding and transient grating shutter according to claim 7, characterized in that: The imaging unit (8) is used to receive each sub-beam after being gated by the transient grating shutter, and form a composite light field image; The data processing unit is used to perform frequency domain analysis on the composite light field image, separate and restore the light field information of each sub-beam at different time slices.

9. A single-shot imaging method based on structured light coding and transient grating shutter, characterized in that: include: S100, using an ultrashort pulse laser (1) to illuminate the transient event device to be measured (2), generating a signal light to be measured that carries information to be measured, and using an optical beam splitter (3) to split the signal light to be measured into a plurality of sub-beams; S200, using an optical path adjustment unit (4) to set different time delays for each sub-beam; S300, performing spatial frequency domain modulation encoding on each sub-beam using gratings at different spatial orientations in a structured light encoding unit (5) to form an encoded sub-beam; S400, combining the encoded sub-beams through an optical beam combiner (6) to form a first combined beam; S500, passing the first combined beam through a transient grating shutter unit (7), and using the transient grating shutter unit (7) to perform gating of different time slices on each encoded sub-beam; S600, directing each selected sub-beam to an imaging unit (8) to form a composite light field image; S700 , using a data processing unit to perform frequency domain analysis on the composite light field image, and to separate and restore the light field information of each sub-beam at different time slices.

10. The single-shot imaging method based on structured light coding and transient grating shutter according to claim 9, characterized in that: The method of using the data processing unit to perform frequency domain analysis on the composite light field image, separating and restoring the light field information of each sub-beam at different time slices, includes: The data processing unit is used to perform Fourier transform, spatial frequency shift, low-pass filtering, and inverse Fourier transform on the composite light field image, thereby separating and restoring the light field information of each sub-beam.

Images